The effect of age on the light scattering characteristics of the eye.

The rising mean age of our population has increased the need for understanding the physiologic consequences of ageing on visual function. Changes due to age were evaluated using a new scatter test implemented on the P_SCAN 100 pupillometer apparatus (Barbur, 1991). The test yields the full scatter function of the eye and also permits simultaneous measurement of pupil size (Barbur et al., 1995). In addition, contrast sensitivity was measured using sine wave gratings. The 28 subjects had a spherical refractive error between +0.50 DS and -0.25 DS, and astigmatism of less than -0.50 DC, V.A. of at least 6/6, and were ophthalmologically normal. To facilitate statistical analysis, subjects were classified into five groups according to age. For younger subjects (under 45 years), k', the integrated straylight parameter, varied little with age. For this group, k' ranged from 4.9 to 8.1. For subjects aged over 45 years, k' increased with age, ranging from 10.7 to 19.7. One way analysis of variance showed Group 5 (60 year olds) to have significantly greater k' than 20, 30, 40 and 50 year olds (P = 0.000). A slight downward shift in the contrast sensitivity function was seen over the age of 45. Significant differences between older and younger subjects were found at spatial frequencies of 3, and 10 cpd (P = 0.081, P = 0.002, respectively). Pupil diameter was found to reduce with age, but there was no significant difference between groups. Therefore, above 45 years, the ageing eye reveals a more rapid increase in forward scatter, and a reduction in contrast sensitivity, despite apparently good visual acuity.